(WXIA) -- On Thursday, with rifles and side arms loaded and drawn, the Johns Creek SWAT team moved in ready to encounter a gunman, who'd already shot three people.

Instead they found a babysitter with a child.

Only the calm restraint of the police prevented the potential for a deadly accident.

"You had 30 or moreSWAT personnel on the way," said a furious Johns Creek Mayor Mike Bodker. "I mean this is a very, very serious incident someone could have gotten hurt. Thank God, no one did."

Police eventually determined that they had been the victims of a "swatter," someone who calls 911 from a real number with a bogus emergency.

Call spoofing may start with a phone, but it ends with a server. That's why the swatters are so hard to trace. They can hide in a trillion gigabytes of zeros and ones in servers in America or abroad.

The tech is simple. Chances are your kids have used it for fun. But in the wrong hands, it is truly dangerous. Ironically, it is technology that police know very well. Because they use it.

"If they want to contact a suspect, they would put maybe a family member's phone number in the caller ID just to get them to answer the telephone," said cyber security expert Greg Evans. "So that same technology can be used for both good and bad." Evans is a computer hacker turned internet security consultant who says using a familiar or legit number adds weight to the prank call.

"It's scary how it works because you trust what your caller id says."

To prove how easy it is, Evans used his software to call my phone with my mother's number, which was displayed with her name on my phone's screen when the call came in.

It's the same technology that sent shock waves through the British media, after reporters there allegedly hacked the phones of everyone from politicians and royals to at least one murdered child.

"And it will put them directly into your voicemail," said Evans. "And they can listen to all your messages. That's exactly what they were doing in Britain; they were checking everybody including the king's, the queen's, and the princes' voicemails."

Evans stresses that people need to use and guard their voicemail passwords. And he has a word of warning for anyone thinking of trying swatting: Don't.

While it's hard to catch the people who do it, it's not at all impossible.